ES2361193T3 - PROCEDURE FOR PRODUCING A MULTI-PAIR BARRIER STRUCTURE FOR A SOLID OXIDE FUEL CELL. - Google Patents

Abstract

The present invention provides a method of producing a multilayer barrier structure for a solid oxide cell stack, comprising the steps of: - providing a metal interconnect, wherein the metal interconnect is a ferritic stainless steel layer; - applying a first metal oxide layer on said metal interconnect; - applying a second metal oxide layer on top of said first metal oxide layer; wherein said second metal oxide layer comprises a mixture of metal oxides having at least two different metal cations, or a mixture of metal oxides having at least two different metal cations and a transition metal oxide; and - reacting the metal oxide in said first metal oxide layer with the metal of said metal interconnect during the SOC-stack initialisation, and a solid oxide stack comprising an anode contact layer and support structure, an anode layer, an electrolyte layer, a cathode layer, a cathode contact layer, a metallic interconnect, and a multilayer barrier structure which is obtainable by the above method and through an initialisation step, which is carried out under controlled conditions for atmosphere composition and current load, which depends on the layer composition facilitating the formation of the desired reaction products as a dense barrier layer without chromium species migrating to the air-electrode.

Description

Technical field

The present invention relates to a process for producing a multilayer barrier structure in a solid oxide cell, such as a solid oxide fuel cell stack (SOFC) or a solid oxide electrolytic cell stack (SOEC), and a multilayer structure that can be obtained by said process, which is especially suitable for use in the oxygen part of the adjacent cells that separates the interconnecting component of said stacks.

Prior art

Solid oxide cells (SOC) in general include cells designed for different applications, such as solid oxide fuel cells (SOFC), or solid oxide electrolytic cells (SOEC). These types of cells are well known in the art. Normally, a solid oxide fuel cell comprises an electrolytic layer sandwiched between two electrode layers. During operation, usually at a temperature of about 500 ° C to about 1100 ° C, one electrode is brought into contact with oxygen or air and the other electrode is in contact with a combustible gas.

Under typical operating conditions, an individual solid oxide fuel cell produces less than 1 volt. To obtain high voltage and power of SOFCs, it is therefore necessary to stack many cells together. Because the manufacturing procedures for SOFC planar stacks comprise the manufacture of individual cells, the cells subsequently obtained are stacked together with additional layers such as interconnections, current collectors, contact layers and seals to form a cell stack. of fuel for the desired application.

One of the problems that limit mass production of fuel cells to an industrial level to date is the high cost of the final cells. Consequently, for fuel cells and electrolysis cells operating in a medium temperature range (approximately 500 ° C to 900 ° C), it has been suggested to employ relatively inexpensive interconnecting metal components that separate individual cells.

Suitable materials for such metallic interconnection layers need to be resistant to oxidation against anode and cathode gases at elevated operating temperatures, and they must also exhibit a thermal expansion coefficient (TEC) that matches the TEC of the ceramic components of the cell. In view of these requirements, chromium oxide forming alloys have been investigated in particular as support materials during the manufacturing process, which will form the ultimate interconnection layer. Said alloys comprise a high chromium content, that is approximately 15 to 22% by weight, which under oxidative conditions migrates to the surface and forms a chromium oxide barrier layer or chromium oxide deposit on the surface that protects the component against additional oxidation. At the same time, said reservoir exhibits a sufficiently high electrical conductivity so as not to impede the overall performance of the device.

However, during the operation of the cell, chromium ions can diffuse from the interconnecting materials containing chromium to the electrode layers to the adjacent air and disadvantageously affect the performance of the catalyst and thereby disadvantageously affect the performance of the cell. over time. This phenomenon is generally known as ’chromium poisoning’. Chromium poisoning is due to the chromium of the metallic interconnection being transported from the metal by means of oxides and oxyhydroxides containing gaseous chromium and by surface diffusion on the metal oxide components that form bridges to electrochemically sites active near or in the air part of the electrode, in which they rapidly deteriorate the electrochemical activity to a considerable extent.

In order to obtain a low electrical resistance and reduce the chromium poisoning of the chromium oxide deposit forming alloys employed as the interconnecting material, it has been suggested to apply a chromium manganese spinel on the top of an oxide layer of chrome. US-A1-2003 / 0059335 for example proposes an iron-based alloy that forms chromium oxide, which comprises 12 to 28% by weight of chromium and small amounts of La, Mn, Ti, Si, and Al. The material It is capable of forming on its surface a spin phase of MnCr2O4 at temperatures of 700 ° C to 950 ° C. The manganese and chromium spinel thus formed is expected to have a slightly lower vaporization pressure for species containing chromium than the chromium itself.

However, it was found that disadvantageously the diffusion of Cr in effect proceeds faster in the spinel of MnCr2O4 than in the chromium layer. Consequently, the formation of a double Cr2O3- (Mn, Cr) 3O4 deposit does not provide any significant increase in the protection from chromium poisoning, as compared to the deposit of pure chromium oxide.

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Different coatings have been described that prevent the development of chromium-containing vapors in the iron-chromium alloy used as the interconnection in the cells in patents and bibliography of scientific journals, for example in Tietz, F. et al. (2004) DE 103 06 649 A1, Tietz, & Zahid (2004) DE 103 06 647 A1, Hilliard

D.B. (2003) US2003194592-A1, Orlovskaya N et al. (2004). J. Am. Cer, Soc 87, pp. 1981-7, Chen, X. et al. (2004) Solid State lonics 176, pp. 425-33. The common coating concept encompasses the formation of a perovskite spinel or layer with its final microstructure at the top of the metal interconnection before insertion into a stack of SOFCs, in which said coating acts as a barrier layer for the chromium migration from the metallic interconnection in the electrode compartment to the air. In order for these coatings to be sufficiently airtight, the adhesion between coating and substrate must be perfect at the beginning as well as in longer terms, that is, after thermal cycling, which places severe limitations on both processing and coincidence. of coefficients of thermal expansion of the layers and steel.

In view of these problems, the reactive coatings offer a better solution since they are transformed into a barrier layer that grows at a high temperature and normally exhibit a more gradual change in the microstructure between the metal substrate and the overlying oxide coating. Reactive coatings as such have been described in, for example, reports on perovskite spinel and coat analysis: Fujiata, K. el al. (2004) J. Power Sources 131, pp. 261-9; and Larring & Norby (2000), J. of the Electrochem. Soc. 147, pp. 3251-6. The disclosed coatings are single phase or single substance coatings, and are applied in order to form an electrically conductive corrosion protective coating on the metal surface. Such coatings contain as little chromium as possible in order to reduce the transport of chromium from the metal surface for as long as possible, and reduce the transport of oxygen from the atmosphere in the metal.

Protective coatings that act as chromium collectors are disclosed, for example, in Jiang S.P et al. (2002) J. Eur. Cer. Soc. 22, pp. 361-73; and Matsuzaki & Yasuda (2001) J of the Electrochem. Soc. 148, pp. A126-31. It is described how the chromium-containing phases precipitate in various air electrode materials and in different electrolyte materials. The interest is particularly focused on the chromium precipitated in the air electrode materials that include LSM and LSCF without cathodic polarization.

It is also revealed that chromium readily bonds with the elements, such as Mn, of the perovskite structure of the LSM cathode, and creates the phases of the well crystalline spinel that can be recovered at the boundary surface between the electrolyte and the air electrode material if the LSM air electrode is exposed in an electrochemical polarization. LSCF air electrodes are not dependent on the electrochemical potential of the electrode, but nevertheless the chromium-containing phases generally precipitate the pore volume of the electrode.

Document DE-C1-19627504 discloses a metal interconnection connected to a multilayer structure, the structure comprising a first layer of metal oxide on said metal interconnection, followed by two ceramic layers on top of said first layer of metal oxide.

WO-A-2006/059943 refers to a fuel cell component consisting of metal base material, wherein said base material is provided with a coating comprising at least one metal layer based on a metal or alloy metallic, and at least one reactive layer containing at least one element or compound that forms at least one mixed oxide complex with the metal or metal alloy when oxidized.

DE-A1-4422624 refers to a method for protecting a chromium-containing surface against the loss of volatile chromium oxides at higher temperatures by applying a protective coating formed of a magnesium chromate on the surface of the metal layer. .

In synthesis, the barrier layers suggested in the prior art so far act to suppress the formation of chromium-containing vapors during the operation of the cell from the beginning, but which also requires additional processing and frequently costs of metal interconnections before its use in a stack of SOFCs, consequently prevents mass production of the stacks. On the other hand, the applied surface coatings must be chemically and thermomechanically compatible with the materials of the metallic interconnection over a wide range of temperatures, that is, operating temperatures of the cell of approximately 500-900 ° C, which severely limits the use of otherwise suitable materials. Finally, although chromium diffusion or initial evaporation can be reduced to some degree, most layers cannot prevent chromium diffusion during the life of the cell and consequently cannot prevent chromium poisoning of the layers of electrode over time.

Consequently, a cost-effective process is still needed to eliminate the evaporation of chromium from the interconnection surface in solid oxide cells, which makes it possible to accommodate chromium vapor species and that minimizes the resistance of electrical contact between the interconnection and the layer of air electrode

In view of the foregoing, the present invention advantageously provides reactive coatings, applied by an economical process, such as spraying a suspension of particles onto the interconnecting surface and / or the air portion of the solid oxide cells before Assembling the cell stack, the coating minimizes the evaporation of chromium from the metal surface once a dense layer has formed, preferably in a chromium-free reaction, with a sufficient layer thickness. At the same time, an overlying coating captures chromium-containing species that diffuse from the metal surface during the initial period before they reach the active locations of the electrode layer in the air.

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The multifunctional coatings of the present invention reduce the problem of chromium poisoning to a technologically insignificant level, while avoiding much more expensive application procedures for applying the coatings with a similar range suggested in the prior art to date, and provide a profitable multilayer barrier structure that extends the life time of an SOC.

Summary of the invention

In view of the disadvantages of the prior art described above, the present invention provides a method for producing a multilayer barrier structure in a solid oxide cell, according to claim 1.

The present invention also provides a multilayer barrier structure, which can be obtained by the above procedure.

The present invention also provides a solid oxide cell comprising an anodic contact layer and support structure, an anodic layer, an electrolytic layer, a cathodic layer, a cathodic contact layer, a metallic interconnection, and the previous barrier structure. multilayer

Preferred embodiments are defined in claims 2 to 10.

In the process of the present invention the heating sequence and the composition of the gas phase, preferably the partial pressure of oxygen, during the initialization of said solid oxide cell is preferably controlled so as to transform the barrier layer into a product of electrically conductive and dense reaction.

Furthermore, the affinity between the electrode to the air and the chromium during the initialization sequence of the previous stack can be reduced by a method, which comprises the step of applying a constant or alternative electrical potential between the electrode to the air and the interconnection.

Preferred embodiments are set forth in the subclaims.

Brief Description of the Figures

Figure 1 illustrates a preferred embodiment of the multilayer structure of the present invention.

Figures 2a and 2b are micrographs showing a cross section of a barrier structure according to the present invention as a function of the thickness of the layer.

Figure 3 is a micrograph showing a cross section of a barrier structure according to the present invention.

Figure 4 illustrates the difference in electrical performance of the degradation rate of a stacking element of similar components with and without the protective coating on the face of the air electrode of the interconnection.

Detailed description of the invention

The present invention provides a method for producing a multilayer barrier structure in a solid oxide cell, comprising the steps defined in claim 1.

With the process of the present invention, a multilayer barrier structure is applied between the metallic interconnection and the air electrode layer in an SOC stack. When the stacking begins, the formation of a thermally grown barrier is facilitated, which in turn minimizes the evaporation of chromium from the interconnecting surface, contains chromium vapor species and at the same time minimizes the resistance of electrical contact between the Two components, interconnection and air electrode.

The metallic interconnection is a layer of ferritic stainless steel. Ferritic steels are comparatively economical and allow profitable large-scale production. According to the invention, the metallic interconnection comprises an alloy of FeCrMx, in which Mx is selected from the group consisting of Ni, Ti, Ce, Mn, Mo, W, Co, La, Y, Al, Nb, or its mixtures The concentrations of Mx in the alloy are preferably in an amount such that it prevents the formation of austenite. Preferably, the concentration of Mx is in the range of 0 to 15% by weight, and more preferably about 0.1 to 10% by weight, based on the total weight of the alloy. The concentration of Mn in the alloy is 0.25% to 0.55% by weight.

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Ferritic steels, exemplified by commercial products such as Crofer 22APU (from Krupp-Thyssen) develop a well-defined double deposit of chromium oxide and a Cr-Mn spinel or a mixed chromium-spinel oxide deposit with a phase separation less obvious, for example in the case of OYC44 (can be obtained from Sandvik) and Hitachi ZMG232 (can be obtained from Hitachi).

The first metal oxide layer can be applied by any suitable procedure known to the experts. Paint for layer spraying or laminating with a tape casting film is preferred.

The first metal oxide layer in the final multilayer barrier structure reacts at least partially with oxygen and the metal elements that diffuse outward form the interconnection during the initialization step, thus forming a continuous transition between the second layer and the Protective chrome deposit formed that grow on the metal surface when subjected to high temperature oxidizing conditions. As illustrated in Figure 1, the first metal oxide layer 2 forms a dense layer of mixed oxide having as low a chromium content as possible, such as a layer of MnCo2O4, in which the Mn of the metal interconnection 1 reacts with the applied cobalt oxide. Said layer thus forms an efficient barrier layer that effectively minimizes the transport of chromium from the metal through the reservoir.

Figure 1 is a schematic illustration of a preferred embodiment of the multilayer structure comprising the metal interconnection 1, a first layer of metal oxide 2, a second layer of mixed metal oxides having a perovskite structure 3, a third layer of oxides mixed metals having perovskite structures 4, and additionally spacers for the admission of air into the air electrode 6, which is deposited in the electrolyte and, optionally, the solid oxide cell holder 7.

The thickness of said first metal oxide layer is preferably in a range of from about 1 to about 20 µm, more preferably from about 3 to about 15 µm.

In order to develop a microstructure with a minimum electrical resistance, that is, in which the first dense layer lacking in chromium has good contact with the second layer, the amount of material of the first layer must be minimized. Conversely, in order to develop a low chromium layer, sufficient amounts of metal oxide should be available, as synthesized in Table 1. It was found that the chromium content falls by a factor of two, that is to say from 0.7 to 0.3, when the thickness of the first layer increases from 7 µm to 15 µm. This is also illustrated with Figures 2a and 2b, which show the microstructure of the resulting coating as a function of the layer thickness of the first coating, 7 µm of Co3O4 (Figure 2a) and 15 µm of Co3O4 (Figure 2b), after 1000 hours at 900 ° C. The 15 µm thick Co3O4 coating has not fully reacted with the steel.

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Table 1

1st layer thickness

2nd layer thickness 500 h 1000 h 2000 h 4000 h

Co3O4, 7µm

LSM, 15µm Cr0.7Mn1.4CO0.8Fe0.1O4  Cr0.7Mn1.6Co0.6Fe0.1O4  Cr0.9Mn1.5Co0.5Fe0.1O4  Cr1,3Mn1,2CO0,5O4

Co3O4 15µm

LSM, 15µm Cr0.3Mn0.9Co1.7Fe0.1O4  Cr0.4Mn0.9Co1.6Fe0.1O4  Cr0.5Mn1.1Co1.4O4  Cr0.7Mn0.8Co1.5O4

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Compensation between the chrome barrier function and the desired microstructure to reduce the electrical resistance is preferably achieved through the addition of more metal oxide in the second layer of multilayer structure while maintaining the thickness of the layer of the First layer at a minimum.

The second metal oxide layer comprises a mixture of a metal oxide having at least two different metal cations and a transition metal oxide. Suitable metal oxides for the oxide layer include oxides selected from the group consisting of alkaline earth metal oxides, preferably magnesium oxide, barium oxide, strontium oxide, calcium oxide, and transition metal oxides, preferably cobalt oxide , manganese oxide, copper oxide, lanthanum oxide, and mixtures thereof.

On the other hand, said metal oxide of the second oxide layer having at least two different metal cations preferably has a perovskite structure and is selected from the group consisting of doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, and their mixtures.

The second metal oxide coating can be applied by any suitable procedure known to the experts. Paint for layer spraying or lamination with a tape casting film is preferred.

The thickness of the second metal oxide layer is preferably in a range of from about 10 to about 30 µm, more preferably from about 15 to about 25 µm.

The second layer of the multilayer barrier structure aids in the formation of the barrier layer, and the chromium-picking materials that are capable of capturing species of chromium-rich vapor that evaporate and migrate from the metal deposit during the first initialization period before forming the first barrier layer completely, and later if a small amount of chromium vapor continuously migrates from the tank. As noted earlier, a single layer is not able to minimize chromium poisoning at a technologically acceptable level.

The process also comprises the step of forming a third layer of metal oxide on top of said second layer of metal oxide. If a third layer of metal oxide is applied, the metal oxide for said third layer is selected from the group consisting of doped lanthanum nickellate, doped lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite, doped cerium, and their mixtures

The third metal oxide coating can be applied by any procedure known to the experts. However, spray paint or laminate with tape casting film is preferred.

The thickness of the third metal oxide layer is preferably in a range of about 10 to about 35 µm, more preferably about 20 to about 30 µm.

The third layer can also act as a current collecting layer directly in contact with the air electrode. In this case, a maximum conductivity is achieved in the plane to distribute the conductivity as evenly as possible to achieve for the third layer.

After applying the respective layers of metal oxide on the metal interconnection, the manufacturing of the stack is completed. More specifically, the contact layers are applied on both sides of the solid oxide cell and the cells and interconnections are assembled in an alternating sequence with interposed sealing components.

Figure 3 illustrates an example of a final multilayer barrier structure. Additionally, the result of a so-called line scan is shown, in which the EDS response of a selected range of chemical elements is recorded along a predefined path of the incoming electronic beam, which has been indicated by the line White continues on the micrograph. The metallic phase, light gray on the left, is covered by a layer of 4-6 µm thick chromium oxide, darker gray, and a 6-10 µm thick layer of a Mn-Co spinel layer formed with only a low chromium oxide concentration, cf. Cr profile of the line scan. The layers have formed in air at 950 ° C after applying a first layer of 10 µm thick cobalt oxide, and reacting cobalt oxide with manganese that diffuses out of the steel that forms the interconnection. The microstructure formed is dense and adheres well to the protective deposit formed between the steel surface and the Mn-Co spinel layer. The second 24 µm thick porous coating is composed of LSM.

The initialization stage of the stacking obtained is carried out at an elevated temperature, preferably at a temperature of at least about 500 ° C, more preferably between about 700 ° C and about 1100 ° C. In addition, the initialization step is carried out under controlled conditions for the atmosphere or current load within the actual ranges that depend on the temperature and the coating material. For example, if the initialization temperature is approximately 950 ° C and the first coating layer is preferably mainly cobalt oxide, the air in the atmosphere can be used directly in combination with a current load of 0.02-0, 1 A / cm2 of fuel cell area, inverted with respect to the direction in a fuel cell. If the initialization temperature is approximately 850 ° C and the first coating layer is preferably cobalt oxide mainly, the partial pressure of oxygen is maintained below about 0.06 bar and combined with said current load.

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During initialization, a reaction occurs between the metallic interconnection and the first layer of metal oxide applied. Preferably, the reaction product of the reaction between the metal oxide of said first metal oxide layer and the metal of the metal interconnection is electrically conductive and dense, more preferably it has a spinel structure.

During the operation of a cell stack, a chromium-rich layer will form directly on the metal surface due to the reaction of the metal with oxygen. However, in the multilayer barrier structure of the present invention, the reaction product of the metal oxide of the first metal oxide with the metallic components of the interconnection forms a chrome-free or low-chromium-free layer, preferably a spinel-free layer of chrome, on top of this. The layer formed by the reaction of the metal oxide of the first metal oxide with the interconnection thus forms a barrier layer that effectively suppresses the transport of chromium from the metal through the layer.

The second metal oxide layer acts as a barrier material for the evaporation and migration of chromium-containing species during cell initialization before completing the formation of the layer formed by the reaction of the metal oxide of the first metal oxide with the interconnection . Consequently, the electrode is effectively protected against chromium poisoning even during cell initialization. In addition, in the event that the chromium-containing species diffuse through the first layer during the operation of the cell at any point in the life of the cell, the second metal oxide layer acts as an additional chromium collector and of this mode effectively protects the electrode layer from chromium poisoning.

In a preferred embodiment, a third layer of metal oxide is applied on top of the second layer of metal oxide. The third metal oxide layer maximizes the contacts in the electrical plane of the barrier layer and the contact with the electrode layer as well as maximizes the chromium surface diffusion from the second metal oxide layer to the electrode to the active air. As a result, the conductivity in the plane increases, chromium poisoning can be suppressed, and the cell duration increases.

The present invention also provides a multilayer barrier structure, which can be obtained by the procedure described above. The multilayer barrier structure is suitable for use in the production of a multilayer barrier structure in a stack of solid oxide fuel cells (SOFC) or a solid oxide electrolytic cell (SOEC).

Advantageously, with the barrier layer of the present invention, chromium poisoning of the electrode layers is effectively suppressed, which increases the life of the cell. At the same time, the barrier layer of the present invention achieves low interfacial resistance so as not to interfere with the overall efficiency of the cell.

The process of the present invention is a simple process for obtaining said barrier layer, and consequently more cost effective than the procedures proposed in the prior art, which employ complicated and expensive production steps, such as plasma spraying and the like.

Moreover, the barrier layer is effectively formed during the initialization of the stack, and thus no separate pretreatment of the interconnection is necessary before incorporation into a cell stack, thus simplifying the manufacturing of the cell. .

Finally, as cheap materials can be used, the components for the barrier layer do not significantly increase the total costs of the cells, instead they allow the mass production of the cells to have a barrier layer against chromium poisoning.

The invention will now be illustrated with reference to the detailed example.

Example

- Preparation of metal interconnections

The interconnection materials of a chromium ferritic steel were cut to mold before treating them with surface coatings. The metal surface oxides of the interconnection inherent in the steel production were removed before coating by uniform sanding of the specimens with 1000 grain Sic paper followed by spraying the surfaces with pressurized air and washing first in acetone and subsequently in ethanol, both through the use of an ultrasonic bath.

-Application of metal oxide coatings

The coatings were applied at room temperature by spraying suspended mixtures of approximately 6-14 vol% of granular powders dispersed in an organic vehicle comprising solvent, dispersant and binder, which were subsequently dried at approximately 50-60 ° C in a air stream.

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Perovskite powder, lanthanum-strontium-manganite (La0,85Sr0,15MnO3), hereinafter referred to as LSM, lanthanum-strontium-cobaltite (La0,84Sr0,16CoO3), hereinafter referred to as LSC and (La0,3Sr0,7CoO3) , hereinafter referred to as LSC ', strontium cobaltite (SrCoO2.5), hereinafter referred to as SC, Lanthanferro-nickellate (LaNi0.59Fe0.41O3-d) hereinafter referred to as LNF and lanthanum-strontium-ferri-cobaltite (La0.6Sr0.4Fe0.8Co0.2O3), hereinafter referred to as SLFC, were produced by the glycine-nitrate route from nitrate solutions [L. A. Chick, L. R. Pederson, G. D. Maupin, J. L. Bates, L. E. Thomas and G. J. Exarhos, Materials Letters, 10, (1990), p. 612], were calcined and ground for a desired grain size distribution (0.8 µm <d50 <5 µm) with ball mill.

Individual oxide oxides 0 (Co3O4, Mn3O4, CuO) were obtained as analytical grade materials from commercial sources and ground in the desired grain size distribution (0.6 µm <d50 <2.5 µm) with mill balls. Grain size distributions were measured with a Beckman coulter I / S particle size analyzer.

- Stacking formation

The coated metal interconnects were stacked alternately with the fuel cells, and glass-based sealing components were supplied between each layer in a SOFC stack, based on a flat cell design.

During initialization, air was supplied to the anode and cathode compartments at flow rates of 5-6 ml / min cm2 of surface area until termination of the binder combustion sequence at 500-650 ° C, after which the composition of the atmosphere differed between the two compartments, exemplified by the reduction of the combined anode and the reaction sequence of the cathode lining, for example at 950 ° C for 2.5 hours, in which dry hydrogen was incorporated into the compartment anodic and air was incorporated into the cathode compartment, while a current load of 0.02-0.1 A / cm2 of area of the fuel cell was passed through the stack, inverted with respect to the direction of a operational fuel cell

- Cell evaluation

After initialization, the stacks were heated to operating temperatures between approximately 650 ° C and approximately 850 ° C, in which the degradation was measured under constant conditions for the specific current load and temperatures for periods between 200 hours and 1500 hours .

Chromium poisoning of the air electrode, when active, caused a significant reduction in the maximum power density within a few hundred hours of initialization, which was observed when uncoated metal interconnections were used as a reference. The degradation was evaluated by impedance spectroscopy and change of the normalized voltage or specific resistance of the area over time. The comparison was made in the uncoated metal parts, the degradation of the stack for example, at 750 ° C reached the range of 10-30% per 1000 hours, and in the metal parts coated with a dense coating of prepared gas-tight oxide with plasma spray of the metal oxide powders on the steel, in which the degradation of the stack was similarly recorded in the range of 0.2-0.5% per 1000 hours, which is also close to the detection limit established through individual test cells similarly but in a chromium-free environment. For multilayer metal parts according to the present invention, the degradation of the stack was similarly measured in the range of 0.2-3% per 1000 hours, cf. figure 4.

Figure 4: Experimental validation of the interconnection coating of reference example 1 by stacking test at 750 ° C for 1000 hours

Reference Example 1

Crofer 22APU was cleaned and coated in suspension with a 7 µm thick cobalt oxide layer (d50 = 2.5 µm), dried and subsequently coated in suspension with a 20 µm thick layer of 90% by weight of LSM and 10% by weight cobalt oxide. With the coated cathode-oriented part of a solid oxide fuel cell (SOFC) and incorporated into a stack of SOFC, the metal part was heated in air flow (5.4 ml / min / cm2 surface area) to 3 ° C per minute at 650 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating under the same conditions at 950 ° C, where it was kept for 3 hours in order to form the layer of spinel barrier on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge, in which the degradation rate, 0.2% per 1000 hours, was evaluated at a current load of 0, 25 A / cm2 of cell area.

Reference Example 2

Sandvik OYC44 was cleaned and coated in suspension with a 7 µm thick cobalt oxide layer and copper oxide (2: 1 weight / weight), dried and subsequently coated in suspension with a 20 µm thick layer 60% by weight LSM 30% by weight LSFC and 10% by weight cobalt oxide. With the coated cathode oriented part of a solid oxide fuel cell and incorporated into a stack of SOFC the metal part was heated in air flow (5.4 ml / min / cm2 surface area) at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating in a mixture of air flow and nitrogen (1:50 vol: vol) at 3 ° C per minute at 950 ° C, in which it was held for 4.5 hours in order to form the spinel barrier layer on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge, while air was incorporated into the cathode compartment.

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Reference Example 3

ZMG232 was cleaned and coated in suspension with a 5 µm thick layer of copper oxide and manganese oxide (4: 1 mol / mol), dried and subsequently coated in suspension with a 25 µm thick layer of 50 % by weight of LSM, 30% by weight of LSC and 20% by weight of cobalt oxide. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated into a stack of SOFCs, the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating in a mixture of air flow and nitrogen (1: 9 vol: vol) at 5 ° C per minute at 950 ° C, in which it was kept for 4 hours in order to form the spinel barrier layer on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (850 ° C) and connected to an electric charge.

Reference Example 4

Crofer 22APU was cleaned and coated in suspension with a 7 µm thick cobalt oxide layer (d50 = 0.6 µm), dried and subsequently coated in suspension with a 90 µm thick layer of 90% in LSM weight and 10% by weight cobalt oxide. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated in a SOFC stack the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn residual organic binder before heating the mixture of air flow and nitrogen (1:30 vol: vol) at 3 ° C per minute at 750 ° C, in which it was maintained for 15 hours in order to form the layer of spinel barrier on the metal surface of the cathode compartment. During this last sequence, a current (0.05 A / cm2) was passed through the stack of SOFCs from the anodic to the cathode terminals. The SOFC stack was then cooled to the operating temperature (650 ° C) and connected to an electric charge, while air was incorporated into the cathodic compartment.

Reference Example 5

Sandviken OYC44 was cleaned and coated in a 10 µm thick layer of cobalt oxide (d50 = 2.51 µm), dried and subsequently coated in suspension with a 30 µm thick layer of 85% by weight LSM and 15% by weight cobalt oxide. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated into a stack of SOFCs, the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn residual organic binder before heating under the same conditions at 1050 ° C, in which it was maintained for 2.5 hours in order to form the spinel barrier layer on the metal surface of the cathodic compartment. The SOFC stack was then cooled to the operating temperature (850 ° C) and connected to an electric charge.

Reference Example 6

A metal part (ZMG232) was cleaned and coated in suspension with a 10 µm thick layer of cobalt oxide and manganese oxide (4: 1 mol / mol), dried and subsequently coated in suspension with a layer of 25 µm thickness of 55% by weight LSC 25% by weight LSC 'and 20% by weight SC. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated into the SOFC stack, the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn residual organic binder before heating in a mixture of air flow and nitrogen (1: 100 vol: vol) at a rate similar to 850 ° C, in which it was maintained for 5 hours in order to form the barrier layer of spinel on the metal surface of the cathode compartment. During this last sequence an alternating current (1 kHz, 0.05 A / cm2) was passed through the stacking of SOFCs between the anode poles to the cathode. The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge.

Reference Example 7

Crofer 22APU was cleaned and coated in suspension with a 5 µm thick layer of cobalt oxide (d50 = 0.6 µm), dried and subsequently coated in suspension with a 25 µm thick layer of 75% in LSM weight, 10% by weight of barium oxide, 10% by weight of calcium carbonate and 5% by weight of magnesium oxide. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated into a stack of SOFCs, the metal part was heated in air flow (5.4 ml / min / cm2 surface area) at 3 ° C by minute at 550 ° C and kept at the temperature for 2 hours to burn residual organic binder before heating under conditions similar to 900 ° C, in which it was maintained for 3.5 hours in order to form the spinel barrier layer on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge.

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Reference Example 8

Sandvik 1C44Mo20 was cleaned and coated in a 10 µm thick layer of cobalt oxide and copper oxide (2: 1 weight / weight), dried and subsequently coated in suspension with a 35 µm thick layer of 90% by weight of LSM and 10% by weight of cobalt oxide. With the coated cathode-oriented part of a solid oxide fuel cell and incorporated in a SOFC stack the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating in airflow at 3 ° C per minute to 950 ° C, where it was maintained for 4.5 hours in order to form the spinel barrier layer on the metal surface of the compartment cathodic The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge, while air was incorporated into the cathode compartment.

Reference Example 9

ZMG232 was cleaned and coated in a 10 µm thick layer of copper oxide, manganese oxide and LSM (16: 4: 1 mol / mol), dried and subsequently coated in suspension with a 25 µm layer thick copper oxide, manganese oxide and LSM (4: 1: 8 mol / mol). With the coated cathode-oriented part of a solid oxide fuel cell and incorporated into a stack of SOFCs, the metal part was heated in air flow at 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating in a mixture of air flow and nitrogen (1: 9 vol: vol) at 5 ° C per minute at 950 ° C, in which it was kept for 4 hours in order to form the spinel barrier layer on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (850 ° C) and connected to an electric charge.

Example 10

Crofer 22APU was cleaned and coated in suspension with a 7 µm thick cobalt oxide layer (d50 = 2.5 µm), dried and subsequently coated in suspension with a mixed 20 µm thick layer of LSM and LSC

(1: 1 p: p). After drying, a third 25 µm thick layer of LNF was applied by casting the suspension and the coated component was further dried. With the coated cathode-oriented part of a solid oxide fuel cell (SOFC) and incorporated into a stack of SOFC, the metal part was heated in air flow (5.4 ml / min / cm2 surface area) to 3 ° C per minute at 550 ° C and kept at the temperature for 2 hours to burn any residual organic binder before heating under the same conditions at 950 ° C, where it was maintained for 3 hours in order to form the layer of spinel barrier on the metal surface of the cathode compartment. The SOFC stack was then cooled to the operating temperature (750 ° C) and connected to an electric charge, in which the degradation rate at a current charge of 0.25 A / cm2 of cell area was evaluated .

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Claims (10)

1. A process for producing a multilayer barrier structure for a solid oxide cell, comprising the steps of:

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 provide a metal interconnection in which the interconnection is a ferritic stainless steel layer and comprises an FeG-Mx alloy, in which Mx is selected from the group consisting of Ni, Ti, Ce, Mu, Mo, W, Co , La, Y, Al, No or mixtures thereof, with a concentration of Mu of 0.25 to 0.55% by weight of the alloy;

-

 applying a first layer of metallic oxide in said metallic interconnection, wherein said first layer of metallic oxide consists of cobalt oxide,

-

 applying a second metal oxide layer on top of said first metal oxide layer, wherein the second metal oxide layer comprises a mixture of a metal oxide having at least two different metal cations and transition metal oxide;

 -

 applying a third layer of metal oxide on top of said second layer of metal oxide;

-

 forming a solid oxide cell comprising said metal interconnection having said layers of metal oxide on it; Y

-

 reacting the metal oxide of said first metal oxide layer with the metal of said metal interconnection during the SOC-initialization of the cell.

2.

 The method of claim 1, wherein the initialization step is carried out at an elevated temperature of at least preferably between 700 ° C and 1100 ° C.

3.

 The method of claim 1 or 2, wherein the reaction product of the reaction between the metal oxide of said first metal oxide layer and the metal of said metal interconnection has a spinel structure.

Four.

 The method of claim 1, wherein in said second metal oxide layer said metal oxide having at least two different metal cations has a perovskite structure and is selected from the group consisting of doped lanthanum manganite, doped lanthanum cobaltite , doped lanthanum ferrite, and mixtures thereof.

5.

 The process of any one of claims 1 to 4 wherein the thickness of said first metal oxide layer is 1 to 20 µm.

6.

 The process of any one of claims 1 to 5, wherein the thickness of said second metal oxide layer is 10 to 30 µm.

7.

 The method of any one of claims 1 to 6, wherein the metal oxide for said third layer is selected from the group consisting of doped lanthanum nickel, nickel oxide, lanthanum manganite, doped lanthanum cobaltite, doped lanthanum ferrite , doped cerium, and mixtures thereof.

8.

 A multilayer barrier structure for solid oxide cells, which can be obtained according to claim 1.

9.

 A stack of solid oxide cells comprising an anodic contact layer and support structure, an anodic layer, an electrolytic layer, a cathodic layer, a cathodic contact layer, a metallic interconnection, and the multilayer barrier structure of the claim 8.

10.

 Use of the multilayer barrier structure of claim 8 as a barrier layer structure in solid oxide fuel cells or solid oxide electrolytic cells.